The embodiments disclosed herein relate to bipolar devices (e.g., bipolar junction transistors (BJTs) and heterojunction bipolar transistors (HBTs)) and, more particularly, to bipolar devices incorporating an entirely monocrystalline link-up region between the intrinsic and extrinsic base layers and to methods of forming such bipolar devices.
As discussed in U.S. Pat. No. 6,972,443 issued on Dec. 6, 2005 to Khater, assigned to International Business Machines Corporation and incorporated herein by reference, it is desirable in bipolar devices, such as bipolar junction transistors (BJTs) and, particularly, in high performance heterojunction bipolar transistors (HBTs), to have a relatively high transit frequency fT and maximum oscillation frequency fmax. fmax is a function of fT and parasitic resistances and capacitances. One such parasitic resistance is the base resistance Rb. Reduction of this base resistance Rb can result in a higher fmax. Thus, it would be advantageous to provide a bipolar device, such as a bipolar junction transistor (BJT) or heterojunction bipolar transistor (HBT), with reduced base resistance Rb and a method for forming such bipolar device.